1. Field of the Invention
This invention relates to a method of welding a sheet steel sheath to a nut body to form a capped wheel nut.
2. Prior Art
Nuts for retaining the wheels of automobiles and other vehicles to the axles are often formed with caps that extend over the end of the nut opposite to the wheel engaging end. These caps serve the functional purpose of preventing exposure of the wheel studs to minimize corrosion or damage that might be caused by impacts, as well as the aesthetic purpose of providing a decorative appearance to the wheel. U.S. Pat. No. 3,364,806 assigned to the assignee of the present invention, discloses a form of capped wheel nut that has enjoyed substantial commercial success. Broadly it employs an ordinary sheet nut body having the wrench flats covered by a sheath of sheet stainless steel. The sheath extends over the end of the nut opposite to the wheel engaging cone and terminates at a land formed between the cone and the adjacent end of the wrench flats.
Repeated applications of wrenching forces to capped nuts of this type may tend to loosen the engagement between the sheath and the nut body causing rattling or complete loss of nut sheath. It has been proposed that the sheath be welded to the nut bodies to eliminate rattling and U.S. Pat. No. 4,123,961 assigned to the assignee of the present invention, discloses a method of welding these nuts involving contacting the exposed conical nut end and the sheath with electrodes, and passing an extremely short duration, high current pulse between the electrodes.
In welding the sheaths to the nut bodies care must be taken to insure that the stainless steel of the sheath is not subjected to temperatures which will adversely affect its coloration or corrosion resistance. If the sheath is exposed to conventional welding temperatures for conventional periods of time, carbon migration will occur and will substantially lower the steel's corrosion resistance resulting in discoloration during use. The welds must also be positioned between the sheath and the body in such a manner that the torquing forces exerted on the weld during wrenching of the nut is not likely to result in rupture of the sheath.